In general, cameras compress video data while capturing videos. Compressing of the video data includes predicting image motion by analyzing a series of image frame data, and encoding the image frame data based on the predicted image motion.
Much computation operations are necessary to analyze the series of image frame data and predict image motion. Therefore, since compression is performed for a relatively long time, transmission of compressed video data may be unstable when the compressed video data is streamed to an external device.
A representative example of a compression method is an encoding method using a group of pictures (GOP) in Motion Pictures Experts Group 1/2 (MPEG-1/2).
For example, when a unit of GOP is 10 image frames, a first image frame is an intra frame, and second to tenth image frames are predicted frames and bidirectional frames.
An intra frame, which is referred to as ‘I frame,’ is a frame in which original image data is internally compressed according to the Joint Photograph Experts Group (JPEG) compression method. The intra frame has a relatively large amount of compressed data
A predicted frame, which is referred to as ‘P frame,’ is obtained by performing various computation operations to analyze image data of previous frames and predict image motion in a current frame, and encoding image data of the current frame based on the predicted motion. Therefore, data of the P frame is less than data of the I frame, but generation time of the P frame is longer than that of the I frame.
A bidirectional frame, which is referred to as ‘B frame,’ is obtained by performing various computation operations to analyze image data of previous frames and image data of following frames and predict image motion of a current frame, and encoding the image data of the current frame based on the predicted motion. Therefore, data of the B frame is less than the data of the P frame, but longer time is consumed to generate the B frame than the P frame.
In summary, longer time is necessary to generate the bidirectional frame, i.e., the B frame, and the predicted frame, i.e., the P frame.
Therefore, in order to compress video data, cameras in the related art require much computation processing to analyze a series of image frame data and predict image motion. Thus, since compression is performed for a relatively long time, transmission of compressed video data may be unstable when the compressed video data is streamed to an external device. Also, restoration time may increase as much as increased compression time.
For example, when a surveillance camera compresses live-view video data and transmits the compressed data to an external device, a user of the external device may not be able to watch a live-view video without buffering.